<div th:replace="~{base :: html(head = null,content = ~{::content})}">
    <th:block th:fragment="content">
        <th:block th:if="${user!=null}">
            <h3>Welcome [[${user.name}]]!</h3>
        </th:block>
        <th:block th:if="${user==null}">
            <h3>Welcome</h3>
        </th:block>
    </th:block>
</div>

